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Re: Part suppliers

Postby Chris » Fri May 17, 2013 10:34 pm

simon wrote:Great. :)
Are you making progress with the V9990? I like it pretty much but it has it's disadvantages...
Lately I am still a bit lazy but read about programming gfx effects. I wonder how much use one can get by using the blitter. It is very fast but not that advanced as the Amiga blitter. BTW my advice is to add direct VRAM access for the CPU. This simplifies framebuffer usage and should speed it up as well. Especially if the CPU is 16Bit.

Simon


Excellent, so we can expect some great c64 type demo's soon? :o

I'm still laying out the main processor and memory interfaces so haven't actually done anything with the chip so far.

I have nearly completed the pcb layout for the 68000, 2 x 8 bit 128KB flash memories , 16MB 72pin simm and glue, its tough routing all those signals on 2 sides only, I can see how it took you a week just to decide where the components went on the pcb. I have rerouted at least 6 times so far and it is only 10 chips! I hope this time is the last, it seems to be flowing nicely.

I was thinking of putting a slot on the pcb for a video adapter so I could make a V9990 card or a tms34010 card but will definately consider the direct addressing of the vram into the ram space for the V9990, although bus sharing with the V9990 may be tricky, do you have any application notes showing best practice for doing this?

I also need to read up on graphics processing.

Chris
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Re: Part suppliers

Postby simon » Sat May 18, 2013 8:31 am

Yes, demos would be nice, but at the moment I would prefer games. So I look in every direction and look for techniques which game designers used in the old days. For example I found a good site which describes pseudo 3D or racing games (like Outrun): http://www.extentofthejam.com/pseudo/

Which software do you use for creating the schematic and PCB? The hardest parts were placing the parts and manually routing the power supply traces. In addition I routed some critical signals by hand as well (RGB for example) before the autoroute took over. At last I let the autorouter run for more than a week. ^^

Oh I am not at home until monday but can give you some tips. There is a pin at the V9990 which indicates that the CPU wants to access the VRAM by itself. The V9990 synchronizes its bus and gives feedback to the CPU via another pin when the bus is free. With some bus buffers and a state maschine this should be rather simple. The drawback is that the handshaking has to be done for every single access. So the CPU can't grab the VRAM bus for burst accesses as the V9990 needs access for video signal creation in time... Maybe one could do some tricks with todays fast devices and squeeze two accesses in the provided time slot. But I never tried this.
There is a single page of timing diagrams in the datasheets which describes this behaviour.

Simon
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Re: Part suppliers

Postby Chris » Sat May 18, 2013 11:24 am

No problem I just got back from a 3 day conference in London myself.

That is a very interesting website, far to much math for me :D I prefer my top down/side scrolling shooters and platform games. a true child of the 70/80's :lol:

I think i see the pins you refer to, VMREQ and VMBG. I have a 123 page datasheet but its not the best I have come across, the VRAM bus arbitration is on page 93, very sparse information. I assume they must have produced a more indepth user guide for it like TI did for the tms34010 but I can't seem to find one.

I use easypc but it's not the best package in the world. The 150Euro autorouter sucks, the first board I tried it routed a 12v rail straight across a poured ground plane effectively shorting them together, i spent hours tweaking settings to keep it out of the poured areas but it ignored everything. I never tried it again! big waste of money IMHO. The 530Euro may be better but I can't justify the cost and to use the online router you used I need to buy the specctra interface option for another 150Euro. So looks like I'm doing it all by hand or learning a new package.

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Re: Part suppliers

Postby simon » Sat May 18, 2013 2:40 pm

Nice, I hope I'll make it to London maybe this autumn. But not for work... :)

Yes, the site has much information. Too much to start with. Probably I'll go for a top-down/right-left scroller too. First something like one of my first racing games from the VIC-20. Skiing and trying not to touch trees or something like that. :)

Right, that are the lines. Unfortunately I never found a more detailed users guide. I wish I had one but if you use a CPLD for the glue you can test ideas quite easy. Just don't forget to implement the bus buffers. The timing can be adjusted later...
But it will be much more complicate if you want to squeeze two accesses into one because even when the V9990 allows the CPU direct VRAM access it never releases RAS and CAS for the VRAM...

Ohh, too bad with your autorouter. Can your software import/export to other formats? Maybe you could export Eagle format and use the free Eagle version to export/import to the needed specctra format. This would be a hack and not very comfortable. But in my opinion a good one to avoid expensive software. Especially if you only need it a few times...

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